JP2566971B2 - Metal recovery method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to the products resulting from the carbonylation process.
Group VIII noble metal catalysts and, optionally, co-promoters and recovering co-promoters. More specifically, the present invention provides a high melting point organic polymer (known in the art as tar) produced by a Group VIII noble metal catalyst and co-promoters and co-promoters as a by-product in such a carbonylation process. Are included in the product stream.

The carbonylation method catalyzed by Group VIII noble metals is
It is well known in the art and some are done commercially. Representative examples of such processes are (a) rhodium-catalyzed hydroformylation of olefins to higher alcohols, aldehydes and ketones, (b) rhodium-catalyzed carbonylation of methanol to acetic acid, (c) methyl acetate to acetic acid. Rhodium-catalyzed carbonylation to anhydride or ethylidene diacetate and (d) Rhodium-catalyzed carbonylation of acetic anhydride and acetic acid formation of methyl acetate, water and methanol as described in EP87870.

A problem often encountered with this type of process is that in addition to the desired product, significant amounts of high molecular weight organic polymers (tars) are often produced as by-products. For commercial plants where the high boilers and catalyst tend to be continuously recycled, the production of such tars is especially undesirable because they tend to deposit in the carbonylation reactor. Therefore, in order to prevent such tar deposition, a side stream is continuously withdrawn from the catalyst recycle stream or carbonylation reactor contents and the tar is removed from the Group VIII noble metal catalyst and co-promoters and co-promoters. It must be treated in such a way that it is separated from The Group VIII noble metal catalyst and co-promoter and co-promoter are then returned directly or indirectly to the carbonylation reactor and the tar can be discarded.

One method of such separation / recovery is to distill the side stream to a solid residue containing primarily Group VIII noble metals, promoters and co-promoters, and then to solubilize the residue such as a strong acid. It is to treat with liquid. The Group VIII noble metal, promoter and co-promoter can be dissolved in the solubilizing liquid and then recovered from the solubilizing liquid using standard techniques. Such a method can, in principle, be used in commercial plants, but it suffers from the disadvantage that it cannot be operated easily and continuously.

Another method that can be operated continuously is described in US Pat. No. 4,388,217. Suitable methods for treating tar produced during the production of acetic anhydride by the reaction of rhodium catalysts, iodide-promoted, lithium co-promoted methyl acetate with carbon monoxide include tar, rhodium catalysts, iodide promoters and It consists of diluting the reactor side stream containing the lithium copromoter with methyl iodide and then contacting it with an aqueous hydroiodic acid solution in a countercurrent extractor. During extraction, rhodium, iodide and lithium migrate to the aqueous phase,
The water immiscible tar and methyl iodide remain as separate organic phases. The two phases are separated after extraction by known methods and the tar is further separated from methyl iodide and then discarded. For hydroiodic acid leaving the extractor, this can be processed to recover the rhodium, iodide and lithium components recycled to the carbonylation reactor.

The process described in U.S. Pat. No. 4,388,217 is efficient and can be used to continuously operate a side stream from a carbonylation reactor or product flash tank, but has certain disadvantages. One disadvantage is that the hydroiodic acid solution stream is highly corrosive and requires the use of special plants. Another disadvantage is the need to recover the rhodium, iodide and lithium components from the aqueous stream. rhodium,
Although it is taught that iodide and lithium value can be recycled directly to the carbonylation reactor, the presence of hydriodic acid leads to the deposition of methyl iodide in the main plant, so , In practice is not desirable. As a result, it is necessary to recover the methyl iodide and convert it to hydroiodic acid, or to use auxiliary equipment to drive off excess iodide from the plant.

A method has now been invented in which Group VIII noble metals and co-promoters and co-promoters can be recovered from tar-bearing streams without the disadvantage of using aqueous hydroiodic acid as the extraction medium. This method is described in U.S. Pat.
Contrary to the teaching of No. 7, it is based on the unexpected finding that efficient extraction can be achieved by using aqueous acetic acid as the extraction medium.

Accordingly, the present invention provides a method for recovering a Group VIII noble metal catalyst from a process stream containing a Group VIII noble metal catalyst derived from a carbonylation step and methyl iodide, the method comprising: Contacting the process stream with an extract stream and then recovering the extract stream under conditions where the extract stream is extracted from the process stream into the extract stream, the extract stream comprising acetic acid in water.

Group VIII noble metals are very well known to those skilled in the art and refer to any one or more of the metals ruthenium, osmium, rhodium, iridium, palladium and platinum. Preferably, the Group VIII noble metal is
Rhodium or iridium, more preferably rhodium.

The process stream optionally comprises catalyst promoters and co-promoters that can be recovered with the Group VIII metal. These are discussed in detail in other patents such as British Patent Nos. 1468940, 1538783, 1233121 and 1253758, and are likewise familiar to those skilled in the art. In the case of rhodium catalysts, halide promoters such as bromide or iodide alone or one or more such as amines, phosphines, arsines, stibines and other metals (eg chromium, zirconium, vanadium, lithium, etc.). Often used with any co-promoter to achieve commercial reaction rates. Single and multiple catalyst / promoter / copromoter systems based on these components can be recovered using the methods described above. The extract stream preferably comprises 30-90% by volume acetic acid in water. 30%
Below the volume, the work rate of acetic acid is reduced to be equivalent to that achieved with water, and above 90% volume, the solubility of methyl iodide in acetic acid water becomes too high for practical purposes. However, within this range it is preferred to operate under conditions such that the ratio of methyl iodide to aqueous acetic acid is the minimum required to maintain phase separation. The extraction solution is preferably pre-saturated with methyl iodide before use.

A process stream containing a Group VIII noble metal catalyst and any promoters and co-promoters that may be present is suitable for the polymerization of tars, especially ketones or the reaction of ketones with methyl acetate, acetic anhydride, ethylidene diacetate, etc. It contains these types of tar. The properties of such tars were discussed by means of NMR spectra, infrared spectra and empirical formulas in US Pat. No. 4,388,217. The process stream is preferably a tar-containing side stream or a recycle stream from a carbonylation reactor or product flash tank, with methyl iodide and optionally water, optionally,
After condensing such a stream to remove volatiles,
Induced by diluting.

The process of the invention is preferably carried out by contacting the process stream and the extraction stream in a countercurrent manner.

After the two streams are brought into contact and the Group VIII metal is extracted, the two streams are separated. The extract stream, which now contains a Group VIII metal catalyst and optionally promoters and co-promoters, is recycled to the carbonylation step, while the process stream, if containing tar, separates tar and methyl iodide. Are supplied to separate units. The methyl iodide can be recycled for reuse and the tar discarded.

The method of the present invention can be performed, for example, as shown in FIG. In this case, the side stream containing the rhodium catalyst, iodide promoter, quaternary amine co-promoter, tar and carbonylation reaction product is removed from the carbonylation step and diluted with methyl iodide. The diluted sidestream is
It is then fed to an extraction column where it is countercurrently contacted with an extraction stream of acetic acid in water. Typically, this is done by feeding a thicker dilute side stream to the top of the column, withdrawing from the bottom, feeding a lighter extract stream to the bottom, and removing at the top. Good contact can be achieved by stirring or by stirring the contents of the column, although axial mixing should be avoided as much as possible.

The dilute side stream, which is now removed from the bottom of the column and now consists of methyl iodide, tar and traces of catalyst, promoter and co-promoter, is fed to a distillation column where methyl iodide is recovered from above and recycled. . Tar residues include, for example:
Discard by burning.

The extract stream removed from the top of the extraction column and now containing most of the catalyst, promoter and co-promoter can be recycled to the carbonylation reaction.

The improved efficiency of extraction obtained with aqueous acetic acid as the extraction stream is illustrated by the examples below.

Example 1 Composition: Methyl iodide 5.3% (by weight) Methyl acetate 6.7% Acetic anhydride 17.1% Acetic acid 35.4% By-product 1.4% N-Methylimidazolium iodide 29.2% Tar 4.8% Rhodium catalyst from carbonyl process with 690ppm. The side stream was continuously mixed with 3.3 ml / min of methyl iodide at a rate of 1 ml / min. Extract the mixture into an extraction column (0.7 QVF tube approximately 125 cm high, and 1.6-
1.8 cm ID), where it was countercurrently contacted with 10.6 ml / min of an extract stream consisting of 77% by volume acetic acid, 23% by volume water at 25 ° C.

The above experiment was conducted for 3.5 hours. Finally, the extraction stream leaving the extraction column and the tar-containing mixture were separately collected and analyzed. Due to atomic absorption, both analyzes show 94% rhodium.
It showed accountability and about 98% rhodium extraction efficiency of the extraction stream.

Example 2 Example 1 was repeated except that the volume of the extraction stream used was 5 ml / min instead of 10.6 ml / min. A series of experiments were carried out using extraction streams of different composition. Rhodium extraction efficiency is graphed in FIG. 2 as a function of extraction flow. The results show that rhodium extraction efficiency increases as the acetic acid content of the extract stream increases. In these experiments, rhodium's red-faced avantavirity was similar to that shown in Example 1.

[Brief description of drawings]

FIG. 1 is a flow chart of the Group VIII noble metal recovery method of the present invention. FIG. 2 is a graph showing the relationship between rhodium extraction efficiency and acetic acid in water.

Claims (10)

(57) [Claims] 1. A VIIIth derivative derived from a carbonylation step.
From a process stream containing a group noble metal catalyst and methyl iodide,
In the method of recovering a Group VIII noble metal catalyst, under conditions where the Group VIII noble metal is extracted from the process stream into an extract stream,
A process as described above, which comprises contacting the process stream with an extract stream and then recovering the extract stream, wherein the extract stream consists essentially of acetic acid in water. 2. A method according to claim 1 wherein the process stream further comprises tar. 3. The method according to claim 1, wherein the Group VIII metal is rhodium or iridium. 4. The method according to claim 1, wherein the Group VIII metal is rhodium. 5. A process stream comprising a bromide promoter, an iodide promoter, an amine co-promoter, a phosphine co-promoter, an arsine co-promoter, a stibine co-promoter, and a metal co-comprising chromium, zirconium, vanadium and lithium. A method according to claim 1 or 2 further comprising one or more promoters or co-promoters selected from the group consisting of promoters. 6. The method of claim 1 wherein the process stream and the extraction stream are contacted in countercurrent contact. 7. The method of claim 2 further comprising the step of recycling the extract stream to the carbonylation process. 8. The process of claim 6 further comprising the step of feeding the process stream to a separation unit where the methyl iodide and tar are separated after it has been separated from the extract stream. 9. A method of recovering a rhodium or iridium catalyst from a process stream comprising rhodium or iridium, tar and methyl iodide, wherein (a) rhodium or iridium is extracted from the process stream into an extract stream,
Contacting the process stream with an extract stream consisting of acetic acid in water, thereby providing an extract stream containing rhodium or iridium and a process stream depleted of rhodium or iridium and containing tar and methyl iodide, b) A method as described above, which then comprises separating the process stream and the extraction stream. 10. A process according to claim 9 wherein the process stream is separated into methyl iodide for recycle and tar for waste.